Reactions of #sigma#-#pi# alkenyl complexes [Fe_2(CO)_6(#mu#-alkenyl)(#mu#-PPh_2)] with bis(diphenylphosphino)methane (dppm); carbonyl substitution, migratory carbonyl insertion, phosphorus-carbon bond formation and cleavage, proton shift and alkenyl

摘要

Products of the thermal reactions of #mu#-alkyl complexes [Fe_2(CO)_6(#MU#-R~1C=CHR~2)(#mu#-PPh_2)] (1), (a, R~1=R~2=H; b, R~1=EtO, R~2=H; c, R~1=H, R~2=Ph; d, R~1=Ph, R~2=H; e, R~1=R~2=Ph; f, R~1=CMe=CH_2, R~2=H), with bis(diphenylphosphino)methane (dppm) are substituent dependent. Complexes 1a-c afford simple substitution products trans-[Fe_2(CO)_4(#mu#-alkenyl)(#mu#-PPh_2)(#mu#-dppm)] (2a-c); while with 1d,e #alpha#,#beta#-unsaturated acyl complexes trans-[Fe_2(CO)_4{#mu#-O=C-C(Ph)=CH(R~2)}(#mu#-PPh_2)(#mu#-dppm)] (3d,e) are the major products formed via a migratory-insertion reaction. A minor product of the reaction with 1d is [Fe_2(CO)_5{#mu#-Ph_2PC(Ph)=CH_2}(#mu#-dppm)] (4), the result of phosphorus-carbon bond formation. Reaction of 1f also leads to phosphorus-carbon bond formation together with a 1,4-proton shift giving the #mu#-alkylidene complex [Fe_2(CO)_4{#mu#-HC-C(Me)=C(Me)PPh_2}(#mu#-dppm)] (5). Dppm addition to 1c has been followed in detail, allowing a complete reaction scheme to be developed. Initial carbonyl substitution affords the #eta#~1-dppm complex [Fe_2(CO)_5(#eta#~1-dppm)(#mu#-HC=CHPh)(#mu#-PPh_2)] (6). This #mu#-alkenyl 2c. Loss of CO from isomeric 3d occurs only upon prolonged thermolysis and also affords 2c, a result of #alpha#,#beta#-alkenyl isomerisation. Further, heating 4 also yields 2c after CO loss, phosphorus-carbon bond cleavage, and alkenyl isomerisation. While the #beta#-substituted phenylethenyl complex 2c is stable to prolonged reflux in toluene, heating isomeric cis-[Fe_2(CO)_4(#mu#-PhC=CH_2)(#mu#-PPh_2)(#mu#-dppm)] (7) results in formation of the 5-electron #mu#-acyl complex [Fe_2(CO)_3{#mu#-O=C-C(Ph)=CH_2}(#mu#-dppm)(#mu#-PPh_)2)] (8); also prepared upon heating 4. Crystal structures have been carried out on 3e and 5.